SE542262C2

SE542262C2 - A method for controlling a powertrain, a control arrangement for controlling a powertrain, a powertrain, a vehicle, a computer program and a computer-readable medium

Info

Publication number: SE542262C2
Application number: SE1750955A
Authority: SE
Inventors: Andreas Szilassy; Christian Wessel; Max Karjalainen
Original assignee: Scania Cv Ab
Priority date: 2017-07-24
Filing date: 2017-07-24
Publication date: 2020-03-31
Also published as: DE102018005614A1; SE1750955A1; DE102018005614B4

Abstract

The invention relates to a method for controlling a powertrain (3) of a vehicle (1), the powertrain (3) comprising: at least one drive axle (10) with at least one drive wheel (8); and at least one auxiliary brake (6) being connected to the at least one drive axle (10), wherein the powertrain (3) is associated with an Anti-lock Braking System (30), the method comprising, when the at least one auxiliary brake (6) is activated: predicting (s101) activation of the Anti-lock Braking System (30); and controlling (s102) the at least one auxiliary brake (6), such that the predicted activation of the Anti-lock Braking System (30) is avoided.

Description

A method for controlling a powertrain, a control arrangement for controlling a powertrain, a powertrain, a vehicle, a computer program and a computer-readable medium TECHNICAL FIELD The present invention relates to a method for controlling a powertrain of a vehicle, a control arrangement, a powertrain comprising such a control arrangement, a vehicle, a computer program and a computer-readable medium. The present invention more specifically relates to a method for controlling a powertrain to reduce the braking distance.

BACKGROUND Vehicles of today may comprise different types of auxiliary brakes supplementing the service brakes of the vehicle, to provide retarding torque to the drive axle(s) of the vehicle and thereby brake the vehicle. Such auxiliary brakes may for example be retarders, engine brakes or electrical machines. Since the auxiliary brakes only provide braking torque to the drive axle(s) and thus the drive wheels of the vehicle, there is an increased risk of skidding in case of large wheel slips. In order to prevent problems with skidding, vehicles typically comprise an Anti-lock Braking System (ABS) or similar, preventing the wheels from locking up when braking and thereby maintaining steering control. In some vehicles the auxiliary brakes are deactivated, and thus provides zero braking torque, when the ABS is activated. After the ABS has been deactivated the auxiliary brakes are controlled to gradually increase the braking torque to prevent that the vehicle loose traction. This may result in an abrupt braking behaviour, which may be perceived as uncomfortable and which may also affect the safety of the vehicle and its surroundings.

Document US2016137179 A1 discloses a system where deactivation of the auxiliary brake system when activating an Anti-lock Braking System is blocked, if it is determined that it is acceptable in terms of safety and/or drivability.

Document US2008269994 A1 discloses a system for overriding activation of an Anti-lock Braking System on a heavy vehicle with an automatic manual transmission when the vehicle is descending a hill with declination that exceeds a predetermined declination value. This way, removal of braking forces while driving downhill is prevented and the driving experience of the driver is improved.

SUMMARY OF THE INVENTION Despite known solutions in the field, it would be desirable to develop a method for controlling a powertrain of a vehicle, which reduces the braking distance, increases the stability and safety of the vehicle and which increases the driving comfort.

An object of the present invention is therefore to achieve a new and advantageous method for controlling a powertrain of a vehicle, which prevents deactivation of an auxiliary brake due to activation of an Anti-lock Braking System.

Another object of the present invention is to achieve a new and advantageous method for controlling a powertrain of a vehicle, which reduces the braking distance of the vehicle, increases the stability and safety of the vehicle and increases the driving comfort.

Another object of the invention is to achieve a new and advantageous control arrangement, a powertrain, a vehicle, a computer program and a computer readable medium which reduces the braking distance of the vehicle, increases the stability and safety of the vehicle and increases the driving comfort.

The herein mentioned objects are achieved by a method for controlling a powertrain of a vehicle, a control arrangement, a powertrain, a vehicle, a computer program and a computer-readable medium according to the independent claims.

Hence, according to an aspect of the present invention a method is provided for controlling a powertrain of a vehicle, the powertrain comprising: at least one drive axle with at least one drive wheel; and at least one auxiliary brake being connected to the at least one drive axle, wherein the powertrain is associated with an Anti-lock Braking System, the method comprising, when the at least one auxiliary brake is activated: - predicting activation of the Anti-lock Braking System by means of tire modelling, including determining a tire model for the at least one drive wheel (8), wherein the tire model describes the relationship between wheel slip and braking force acting on the at least one drive wheel (8), the tire model depending on at least one of the following parameters: tire properties, road surface condition and vehicle motion; and - controlling the at least one auxiliary brake, such that the predicted activation of the Anti-lock Braking System is avoided.

In order to prevent uncontrolled skidding, vehicles typically comprise an Antilock Braking System (ABS) preventing the wheels from locking up when braking and thereby maintaining steering control. Thus, the Anti-lock Braking System of the invention may be referred to as a system for prevention of wheel lock when braking the vehicle. The Anti-lock Braking System is suitably configured to be activated based on parameters relating to the traction of the wheels, such as wheel slip. Wheel slip depends on the relationship between the rotational speed of the drive wheels and the free-rolling speed. The Anti-lock Braking System is suitably configured to deactivate the at least one auxiliary brake when the Antilock Braking System is activated. By deactivating the auxiliary brake, no braking torque is provided by the auxiliary brake to the at least one drive axle. After the Anti-lock Braking System has been deactivated the auxiliary brake may be controlled to gradually increase the braking torque again. These abrupt changes in braking torque may be perceived as uncomfortable and may also affect the safety of the vehicle depending on the situation. By predicting activation of the Anti-lock Braking System the auxiliary brake can be controlled, such that the predicted activation of the Anti-lock Braking System is prevented. Thus, the auxiliary brake can be controlled to affect the traction of the drive wheels and thereby avoid a situation where the Anti-lock Braking System normally is activated. By avoiding activation of the Anti-lock Braking System, the auxiliary brake is not deactivated and a more even/consistent braking torque is provided to the drive wheels. Hence, by actively avoiding activation of the Anti-lock Braking System and thereby deactivation of the auxiliary brake, the braking distance can be reduced and the stability and safety of the vehicle is increased. Furthermore, the driving comfort is increased.

An auxiliary brake is herein defined as a brake configured for indirectly braking the drive wheel of at least one drive axle. The auxiliary brake is thus distinguished from a service brake of the vehicle which directly brakes any of the wheels of the vehicle. The auxiliary brake may be defined as a nonmechanical brake. The auxiliary brake is suitably adapted to be deactivated when the Anti-lock Braking System is activated. The auxiliary brake being activated means that the auxiliary brake provides a braking torque to the drive axle. The at least one auxiliary brake may be a retarder, an engine brake, an electrical machine in a hybrid vehicle or similar. It is to be understood that the method according to the invention is applicable for more than one auxiliary brake. The method according to the invention may thus be applicable for controlling a powertrain with an auxiliary brake system comprising a plurality of auxiliary brakes.

The method may comprise to predict an imminent activation of an Anti-lock Braking System.

According to an embodiment of the invention predicting activation of the Antilock Braking System comprises predicting when the wheel slip of the at least one drive wheel is such that the Anti-lock Braking System will be activated. Thus, the method may comprise to predict activation of the Anti-lock Braking System based on the wheel slip of the at least one drive wheel. Controlling the auxiliary brake to avoid the predicted activation of the Anti-lock Braking System may thereby comprise to control the auxiliary brake, such that the wheel slip of the at least one drive wheel does not reach a wheel slip value causing activation of the Anti-lock Braking System. According to an embodiment of the invention predicting activation of the Anti-lock Braking System comprises predicting a situation where the at least one drive wheel would lock up. Since the purpose of the Anti-lock Braking System is to prevent wheels from locking up, predicting a situation where the drive wheels would lock up is in this case essentially equivalent to predicting activation of the Anti-lock Braking System.

According to an embodiment of the invention predicting activation of the Antilock Braking System comprises determining a prevailing wheel slip of the at least one drive wheel and comparing the determined wheel slip with a predetermined wheel slip threshold value. The prevailing wheel slip may be measured. The predetermined wheel slip threshold value may correspond to a wheel slip value causing activation of the Anti-lock Braking System. The predetermined wheel slip threshold value may be a wheel slip value somewhat lower than a wheel slip value causing activation of the Anti-lock Braking System. If the determined prevailing wheel slip is lower, but not far from, the predetermined wheel slip threshold value the auxiliary brake may be controlled to avoid activation of the Anti-lock Braking System. Thus, if the determined prevailing wheel slip is lower, but not far from, the predetermined wheel slip threshold value the auxiliary brake may be controlled, such that the wheel slip of the at least one drive wheel does not reach the predetermined wheel slip threshold value. According to an embodiment of the invention the method may comprise to determine a prevailing wheel slip of the at least one drive wheel and comparing the determined (measured) wheel slip with a first wheel slip threshold value and a second wheel slip threshold value. In this case, the first wheel slip threshold value is suitably lower than the second wheel slip threshold value. The auxiliary brake may be controlled in a first way when the first wheel slip threshold value has been reached and the auxiliary brake may be controlled in a different way when the second wheel slip threshold value has been reached. The second wheel slip threshold value may in this case correspond to a highest possible braking force that can be achieved without activating the Anti-lock Braking System.

According to an embodiment of the invention the activation of the Anti-lock Braking System is predicted by means of tire modelling. A tire model describes the relationship between wheel slip and braking force acting on the wheel. Thus, activation of the Anti-lock Braking System may be predicted by means of tire models for the drive wheels of the vehicle. The normal behaviour for a tire on asphalt is that the wheel slip increases with the braking force up to a certain slip value, after which the braking force decreases to a certain level and the wheel slip goes to infinity. The slip value after which the braking force decreases may be referred to as the optimal slip value and the braking force at this point may be referred to as the maximum braking force. The tire model may vary depending on a lot of different parameters, such as tire properties, road surface condition and vehicle motion. When braking a vehicle it is normally desired to achieve the optimal slip value and thus the maximum braking force to reduce the braking distance. By using tire modelling according to the invention it is determined/estimated how the wheel slip of the drive wheel is changing with the braking force and it can thereby be predicted when the wheel slip will be such that the Anti-lock Braking System is activated.

According to an embodiment of the invention the tire modelling comprises estimation of tire stiffness, a prevailing braking force, a prevailing wheel slip of the at least one drive wheel, friction and/or a rotational speed of the at least one drive wheel. The method may thus comprise to estimate the tire stiffness, to determine a prevailing braking force acting on the drive wheel, determine a prevailing wheel slip, determine the friction against the road surface and/or determine the rotational speed of the drive wheel. By use of this information the tire model can be determined and activation of the Anti-lock Braking System can be predicted. Estimation of the tire stiffness may comprise to determine the relationship between the wheel slip of the at least one drive wheel and the braking force. The prevailing braking force acting on the drive wheel, the prevailing wheel slip, the friction and the rotational speed of the drive wheel may be estimated/determined by means of various sensor means such as accelerometers, speed sensors etc. according to conventional methods. The friction between the drive wheels and the road surface may for example be estimated based on the vehicle mass and the inclination of the road.

According to an embodiment of the invention the auxiliary brake is controlled to provide a target braking force. The target braking force is suitably the highest possible braking force that can be achieved without activating the Anti-lock Braking System. As previously discussed with regard to the tire model there is a relationship between wheel slip and braking force acting on the drive wheel. Thus, the target braking force may be the highest possible braking force corresponding to a wheel slip, which would not activate the Anti-lock Braking System. The Anti-lock Braking System may be configured to be activated when the wheel slip is within a certain range. This may be defined by the operating range of the Anti-lock Braking System. By using the tire model of the drive wheels and knowing the Anti-lock Braking System operating range, a wheel slip outside the operating range of the Anti-lock Braking System, which corresponds to a highest possible braking force, can be determined. Thus, the target braking force can be determined by means of the tire model and the operating range of the Anti-lock Braking System. By controlling the auxiliary brake to the target braking force, the predicted activation of the Anti-lock Braking System can be avoided and a consistent highest possible braking force will be applied on the at least one drive wheel. A higher average braking force will thus be applied on the drive wheel and the braking distance will be reduced.

According to an embodiment of the invention the auxiliary brake is controlled, such that the wheel slip of the drive wheel is reduced and/or maintained constant. Alternatively or additionally, the auxiliary brake is controlled, such that the rate of increase of wheel slip of the drive wheel is decreased. According to an example the auxiliary brake is controlled, such that the rate of increase of wheel slip is decreased when the prevailing wheel slip has reached a first wheel slip threshold value, and such that the wheel slip is maintained constant when the prevailing wheel slip has reached a second wheel slip threshold value. The second wheel slip threshold value may correspond to the target braking force.

According to an aspect of the invention a control arrangement for controlling a powertrain of a vehicle is provided, the powertrain comprising: at least one drive axle with at least one drive wheel; and at least one auxiliary brake being connected to the at least one drive axle, wherein the powertrain is associated with an Anti-lock Braking System. The control arrangement comprising: - means for, when the at least one auxiliary brake is activated, predicting activation of the Anti-lock Braking System, including determining a tire model for the at least one drive wheel (8), wherein the tire model describes the relationship between wheel slip and braking force acting on the at least one drive wheel (8), the tire model depending on at least one of the following parameters: tire properties, road surface condition and vehicle motion; and - means for controlling the at least one auxiliary brake, such that the predicted activation of the Anti-lock Braking System is avoided.

It will be appreciated that all the embodiments described for the method aspect of the invention are also applicable to the control arrangement aspect of the invention. That is, the control arrangement may be configured to perform any one of the steps of the method according to various embodiments described herein.

The means for, when the at least one auxiliary brake is activated, predicting activation of the Anti-lock Braking System; and the means for controlling the at least one auxiliary brake, such that the predicted activation of the Anti-lock Braking System is avoided may e.g. be different software modules/portions in a control unit, algorithms, program code or similar.

According to an aspect of the invention a powertrain is provided, the powertrain comprising at least one drive axle with at least one drive wheel; and at least one auxiliary brake connected to the at least one drive axle, wherein the powertrain is associated with an Anti-lock Braking System. The powertrain further comprises a control arrangement as mentioned above.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas embodiments of the invention are described below, it should be noted that it is not restricted to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment of the invention; Figure 2 schematically illustrates a powertrain according to an embodiment of the invention; Figure 3 illustrates a flow chart for a method for controlling a powertrain according to an embodiment of the invention; Figure 4a-c illustrate diagrams over braking force and wheel slip according to embodiments of the invention; and Figure 5 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 schematically shows a side view of a vehicle 1 according to an embodiment of the invention. The vehicle 1 has a powertrain 3 comprising an engine 2 and a transmission 4 connected to the engine 2. The transmission 4 is connected to the drive axles 10 and the drive wheels 8 of the vehicle 1 via an output shaft of the transmission (not shown). The vehicle 1 may further comprise at least one auxiliary brake 6 connected to the drive axles 10 and thus the drive wheels 8. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be a passenger car.

Fig. 2 schematically illustrates a powertrain according to an embodiment of the invention. The powertrain may be a powertrain 3 of a vehicle 1 as disclosed in Figure 1. The powertrain 3 may comprise a combustion engine 2 and a gearbox 4 comprising an input shaft 5. The powertrain 3 may comprise an arrangement 7 for selectively transferring torque between the combustion engine 2 and the input shaft 5. In this figure the torque transferring arrangement 7 is illustrated as a clutch but the powertrain 3 may comprise any other arrangement for selectively transferring torque between the combustion engine 2 and the gearbox 4. The gearbox 4 also comprises an output shaft 20 connected to the drive axle 10 and thus the drive wheels 8. It is to be understood that even though only one drive axle 10 and two drive wheels 8 are illustrated in this figure, the powertrain 3 could comprise several drive axles 10, each having two or four drive wheels 8.

The powertrain 3 further comprises an auxiliary brake 6 connected to the drive axle 10 and the drive wheels 8. The auxiliary brake 6 is a brake configured for indirectly braking the drive wheels 8. In this figure the auxiliary brake 6 is illustrated as a retarder arranged in connection to the output shaft 20 of the gearbox 4, suitably via a gear arrangement. However, the auxiliary brake 6 may be an engine brake, an electrical machine or similar. The powertrain 3 may comprise a plurality of auxiliary brakes 6, which together may be referred to as an auxiliary brake system.

The powertrain 3 is associated with a system 30 for prevention of wheel lock when braking the vehicle. Such a system 30 is herein referred to as an Anti-lock Braking System. The Anti-lock Braking System 30 is suitably configured to be activated based on parameters relating to the traction of the wheels, such as wheel slip. The auxiliary brake 6 is suitably adapted to be deactivated when the Anti-lock Braking System 30 is activated, such that no braking torque is provided to the drive wheels 8.

The powertrain 3 also comprises a control arrangement 40 for controlling the powertrain 3. The control arrangement 40 may comprise at least one control unit 42 and a computer 44 connected to the control unit 42. The auxiliary brake 6 is arranged in communication with the control arrangement 40. The control arrangement 40 may be configured to, when the auxiliary brake 6 is activated, predict activation of the Anti-lock Braking System 30 and control the auxiliary brake 6 such that the predicted activation of the Anti-lock Braking System 30 is avoided.

Figure 3 illustrates a flow chart for a method for controlling a powertrain of a vehicle according to an embodiment of the invention. The powertrain may be the powertrain 3 as disclosed in Figure 2 and the vehicle may be the vehicle 1 as disclosed in Figure 1. The powertrain 3 may thus comprise at least one drive axle 10 with at least one drive wheel 8; and at least one auxiliary brake 6 being connected to the at least one drive axle 10, wherein the powertrain 3 is associated with an Anti-lock Braking System 30. The method comprises, when the at least one auxiliary brake 6 is activated: predicting s101 activation of the Anti-lock Braking System 30; and controlling s102 the at least one auxiliary brake 6 such that the predicted activation of the Anti-lock Braking System 30 is avoided.

The method may comprise to predict s101 an imminent activation of an Anti-lock Braking System 30.

The step of predicting s101 activation of the Anti-lock Braking System 30 may comprise predicting when the wheel slip of the at least one drive wheel 8 is such that the Anti-lock Braking System 30 will be activated. Thus, the activation of the Anti-lock Braking System 30 may be predicted s101 based on the wheel slip of the at least one drive wheel 8.

The step of predicting s101 activation of the Anti-lock Braking System 30 may comprise determining a prevailing wheel slip of the at least one drive wheel 8 and comparing the determined wheel slip with a predetermined wheel slip threshold value. The prevailing wheel slip may be measured. The predetermined wheel slip threshold value may correspond to a wheel slip causing activation of the Anti-lock Braking System 30. The predetermined wheel slip threshold value may be a wheel slip value somewhat lower than a wheel slip causing activation of the Anti-lock Braking System 30. If the measured prevailing wheel slip is lower, but not far from, the predetermined wheel slip threshold value the auxiliary brake 6 may be controlled, such that the wheel slip of the at least one drive wheel 8 does not reach the predetermined wheel slip threshold value. The prevailing wheel slip is suitably determined continuously.

The step of predicting s101 activation of the Anti-lock Braking System 30 may comprise to determine a prevailing wheel slip of the at least one drive wheel 8 and comparing the determined (measured) wheel slip with a first wheel slip threshold value and a second wheel slip threshold value. In this case, the first wheel slip threshold value is suitably lower than the second wheel slip threshold value. The auxiliary brake 6 may be controlled in a first way when the first wheel slip threshold value has been reached and the auxiliary brake 6 may be controlled in a different way when the second wheel slip threshold value has been reached. The second wheel slip threshold value may in this case correspond to a highest possible braking force that can be achieved by means of the auxiliary brake 6 without activating the Anti-lock Braking System 30.

The step of predicting s101 activation of the Anti-lock Braking System 30 may comprise tire modelling. A tire model describes the relationship between wheel slip and braking force acting on the wheel 8. Thus, activation of the Anti-lock Braking System 30 may be predicted by means of a tire model for the at least one drive wheel 8 of the vehicle 1. The method may thus comprise to determine a tire model. The tire modelling may comprise to estimate the tire stiffness, to determine a prevailing braking force acting on the drive wheel 8, determine a prevailing wheel slip of the drive wheel 8, determine the friction between the drive wheel 8 and the road surface and/or determine the rotational speed of the drive wheel 8. By use of this information the tire model can be determined and activation of the Anti-lock Braking System 30 can be predicted. The tire model is suitably determined by means of various sensor means such as accelerometers, speed sensors etc. already available in the vehicle 1.

The step of controlling s102 the auxiliary brake 6 may comprise to control the auxiliary brake 6 to affect the wheel slip of the drive wheel 8. The step of controlling s102 the auxiliary brake 6 may comprise to control the auxiliary brake 6, such that the wheel slip of the drive wheel 8 does not reach a value that would activate the Anti-lock braking system 30. The step of controlling s102 the auxiliary brake 6 may comprise to control the auxiliary brake 6, such that the wheel slip of the drive wheel 8 is reduced and/or maintained constant. Alternatively or additionally, the auxiliary brake 6 is controlled, such that the rate of increase of wheel slip of the drive wheel 8 is decreased.

The step of controlling s102 the auxiliary brake 6 may comprise to control the auxiliary brake 6 to provide a target braking force. The target braking force is suitably the highest possible braking force that can be achieved by means of the auxiliary brake 6 without activating the Anti-lock Braking System 30.

How the auxiliary brake 6 can be controlled and how the target braking force is determined will be further described with regard to Figures 4a-c.

The method may be performed by the control arrangement 40 as disclosed in figure 2.

Figures 4a-c illustrates diagrams of braking force F and wheel slip S according to embodiments of the invention. The diagrams relate to the powertrain 3 as disclosed in figure 2 and the method as described in figure 3 and serve to further explain the invention.

Figure 4a illustrates a tire model according to an embodiment of the invention. The tire model describes the relationship between wheel slip S and braking force F acting on a drive wheel 8. Activation of the Anti-lock Braking System 30 may be predicted by means of such a tire model. The model shows a typical behaviour for a tire on asphalt where the wheel slip S increases with the braking force F up to a certain slip value, after which the braking force F decreases to a certain level. The braking force F provided before the decrease may be referred to as the maximum braking force Fmax and the corresponding wheel slip may be referred to as the optimal slip value Soptimai. It is often desired to provide the maximum braking force Fmax. The tire model, and thus the maximum braking force Fmax and the optimal slip value Soptimai, may be determined by means of estimating the tire stiffness, determining the prevailing braking torque/force acting on the drive wheel 8, determining the prevailing wheel slip S of the drive wheel 8, determining the friction between the drive wheel 8 and the road surface and/or determining the rotational speed of the drive wheel 8.

The dotted line illustrates the point where the Anti-lock Braking System 30 normally is activated. Thus, the Anti-lock Braking System 30 is configured to be activated at a certain wheel slip/braking force, which is defined by the operating range of the Anti-lock Braking System 30. The operating range of the Anti-lock Braking System 30 is suitably known and stored in the vehicle 1. By using the tire model and by knowing the operating range of the Anti-lock Braking System 30, activation of the Anti-lock Braking System 30 can be predicted in a very reliable way. Also, by using the tire model and knowing the operating range of the Anti-lock Braking System 30, a wheel slip S outside the operating range of the Anti-lock Braking System 30, corresponding to a highest possible braking force, can be determined. The highest possible braking force without activating the Anti-lock Braking System 30 may be referred to as a target braking force F target. The target braking force Ftargetmay thus be determined from the tire model and the operating range of the Anti-lock Braking System 30. The auxiliary brake 6 is suitably controlled to the target braking force Ftargetto avoid activation of the Anti-lock Braking System 30 and thereby achieve a higher and more consistent braking force on the drive wheels 8.

In figure 4b the diagram shows an example of how the braking force F provided by the auxiliary brake 6 may change over time. The dashed line shows a situation where the auxiliary brake 6 is deactivated when the Anti-lock Braking System 30 is activated. In this example, the Anti-lock Braking System 30 is configured to be activated when the wheel slip has reached a certain value corresponding to a certain braking force F (here marked with ABS). The braking force F provided by the auxiliary brake 6 is thus decreased to zero and no braking force F is applied on the driving wheels 8. After operation of the Antilock Braking System 30 the auxiliary brake 6 is controlled to gradually increase the braking force provided to the drive wheels 8.

The solid line illustrates the braking force F provided by the auxiliary brake 6 according to the inventive method as disclosed in figure 3. Thus, activation of the Anti-lock Braking System 30 is predicted and avoided by controlling the auxiliary brake 6, such that the braking force/wheel slip does not reach the value where the Anti-lock Braking System 30 is activated. As illustrated by the solid line a more consistent braking force F will thereby be applied to the drive wheels 8. The constant braking force F provided by the auxiliary brake 6 in this figure may correspond to the target braking force Ftargetas mentioned in figure 4a.

Figure 4c illustrates the change of wheel slip S over time t according to an embodiment of the invention. The figure illustrates a situation where the prevailing wheel slip S is continuously determined and where the auxiliary brake 6 is controlled, such that the rate of increase of wheel slip is decreased when the prevailing wheel slip S has reached a first wheel slip threshold value Th1 and such that the wheel slip is maintained constant when the prevailing wheel slip S has reached a second wheel slip threshold value Th2. The second wheel slip threshold value Th2 is suitably lower than the wheel slip value activating the Anti-lock Braking System 30 (here marked as ABS). The second wheel slip threshold value Th2 may correspond to the target braking force Ftargetas mentioned in figure 4a.

Figure 5 is a diagram of a version of a device 500. The control unit 42 and/or computer 44 described with reference to Figure 2 may in a version comprise the device 500. The term “link” refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a nonphysical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer programme, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer programme P which comprises routines for controlling a powertrain of a vehicle. The computer programme P comprises routines for predicting activation of an Anti-lock Braking System of the vehicle. The computer programme P comprises routines for controlling at least one auxiliary brake 6, such that the predicted activation of the Anti-lock Braking System is avoided. The computer programme P comprises routines for predicting said activation by means of tire modelling. The computer programme P comprises routines for determining a target braking force and controlling the auxiliary brake to provide such target braking force.

The programme P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the programme stored in the memory 560 or a certain part of the programme stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the programme stored in the memory 560 or the read/write memory 550. When the device 500 runs the programme, methods herein described are executed.

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

1. A method for controlling a powertrain (3) of a vehicle (1), the powertrain (3) comprising: at least one drive axle (10) with at least one drive wheel (8); and at least one auxiliary brake (6) being connected to the at least one drive axle (10), wherein the powertrain (3) is associated with an Anti-lock Braking System (30), the method being characterised by comprising, when the at least one auxiliary brake (6) is activated: - predicting (s101) activation of the Anti-lock Braking System (30) by means of tire modelling, including determining a tire model for the at least one drive wheel (8), wherein the tire model describes the relationship between wheel slip and braking force acting on the at least one drive wheel (8), the tire model depending on at least one of the following parameters: tire properties, road surface condition and vehicle motion; and - controlling (s102) the at least one auxiliary brake (6), such that the predicted activation of the Anti-lock Braking System (30) is avoided.

2. The method according to claim 1, wherein predicting (s101) activation of the Anti-lock Braking System (30) comprises predicting when the wheel slip of the at least one drive wheel (8) is such that the Anti-lock Braking System (30) will be activated.

3. The method according to claim 1 or 2, wherein the tire modelling comprises estimation of tire stiffness, a prevailing braking force, a prevailing wheel slip of the at least one drive wheel (8), friction and/or a rotational speed of the at least one drive wheel (8).

4. The method according to any one of the preceding claims, wherein the auxiliary brake (6) is controlled to a target braking force (Ftarget).

5. The method according to any of the preceding claims, wherein the auxiliary brake (6) is controlled, such that the wheel slip of the at least one drive wheel (8) is reduced and/or maintained constant.

6. The method according to any of the preceding claims, wherein the auxiliary brake (6) is controlled, such that the rate of increase of wheel slip of the at least one drive wheel (8) is decreased.

7. A computer program (P) comprising instructions which, when the program is executed by a computer (44; 500), cause the computer (44; 500) to carry out the method according to any one of the preceding claims.

8. A computer-readable medium comprising instructions, which when executed by a computer (44; 500), cause the computer (44; 500) to carry out the method according to any one of claims 1-6.

9. A control arrangement (40) for controlling a powertrain (3) of a vehicle (1), the powertrain (3) comprising: at least one drive axle (10) with at least one drive wheel (8); and at least one auxiliary brake (6) being connected to the at least one drive axle (10), wherein the powertrain (3) is associated with an Anti-lock Braking System (30), the control arrangement (40) being characterised by comprising: - means (42, 44, 500) for, when the at least one auxiliary brake (6) is activated, predicting activation of the Anti-lock Braking System (30) by means of tire modelling, including determining a tire model for the at least one drive wheel (8), wherein the tire model describes the relationship between wheel slip and braking force acting on the at least one drive wheel (8), the tire model depending on at least one of the following parameters: tire properties, road surface condition and vehicle motion; and - means (42, 44, 500) for controlling the at least one auxiliary brake (6), such that the predicted activation of the Anti-lock Braking System (30) is avoided.

10. A powertrain (3) comprising at least one drive axle (10) with at least one drive wheel (8); and at least one auxiliary brake (6) being connected to the at least one drive axle (10), wherein the powertrain (3) is associated with an Antilock Braking System (30), characterized in that the powertrain (3) comprises a control arrangement (40) according to claim 9.

11. A vehicle (1) comprising a powertrain (3) according to claim 10.